Air pollutants Unit Conversion

The following is with reference to Air Pollutants,

(* means multiplication and,  / means division)

ppb :-   parts per billion by volume
ppm :-  parts per million by volume

Numbers

Million = 1,000,000

Billion = 1,000,000,000

Trillion = 1,000,000,000,000

1 ppm = 1000 ppb = 10^{3 ppb}
1 ppb = 0.001 ppm = 10^-3 ppm
1% = 10000 ppm
% = ppm * 10^{-4
% = (}10^{3 ppb *}10^{-4) = (ppb/10)}
 %= ppm * 10^-4 = ppb * 10<sup>-1

For concentrations  (of chemical contaminants or soil contaminants)  in water, in soil
the following holds true</sup>

1 ppm = (1 mg/Lit, like in water)= (1 mg/Kg, like for concentrations in soil) = (1gm/m³  like for concentration of chemicals in water)

same for ppb,

1 ppb = 1μg/Lit  = 1 μg/Kg = mg/m³ 

But for concentration of air pollutants in Air, following conversion formula is to be used,

mg/m³  is same as  mg/Nm^3
μg/m3  is same as  μg/Nm³

mg/Nm³ = (ppm * MW )/(0.08205 * °K)

where °K is Deg Kelvin and MW is 
molecular wt. of air pollutants

At 1 atm pressure and 25°C, the above equation becomes

mg/Nm³  = (ppm* MW)/24.45

or

μg/Nm³  = (ppb* MW)/24.45

Standard molar volume of an ideal gas at 1 atm pressure and 25°C temp = 24.45 m³/mol

and at 0°c this volume is 22.414 m³/mol